Envelope regulation in a frequency-modulated continuous-wave radar system

ABSTRACT

A radar system that can block false echoes includes: a local oscillator configured to generate a chirp signal comprising a plurality of chirps, each having a corresponding envelope; a transmitter configured to transmit a signal corresponding to the chirp signal; and a modulation circuit configured to modulate the transmitted signal by regulating a magnitude of one or more portions of the chirp envelopes in a predetermined pattern such that the radar system can discern false echoes which do not match the pattern.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority benefit of U.S. provisional applicationNo. 62/817,035, which was filed on Mar. 12, 2019, and which is entirelyincorporated by reference herein.

FIELD

This application pertains generally to frequency-modulatedcontinuous-wave radar systems. This application pertains particularly tofrequency-modulated continuous-wave radar systems in which chirp signalenvelopes are regulated so as to attend to interference.

BACKGROUND

In the quest for ever-safer and more convenient transportation options,many car manufacturers are developing self-driving cars which require animpressive number and variety of sensors, often including arrays ofacoustic and/or electromagnetic sensors to monitor the distance betweenthe car and any nearby persons, pets, vehicles, or obstacles. Attemptsto detect and mitigate the effects of interference have not been whollysatisfactory. Thus, there is room for improvement in the art.

SUMMARY

In accordance with an example of this disclosure, a transceiver systemcomprises: a local oscillator configured to generate a chirp signal,wherein the chirp signal comprises a plurality of chirps, and whereineach of the chirps has a corresponding envelope; a transmitter, whereinthe transmitter is configured to transmit a signal corresponding to thechirp signal; and a modulation circuit, wherein the modulation circuitis configured to modulate the transmitted signal by regulating amagnitude of one or more portions of the chirp envelopes in apredetermined pattern.

In accordance with another example of this disclosure, a signalmodulation method comprises: generating a chirp signal using a localoscillator, wherein the chirp signal comprises a plurality of chirps,and wherein each of the chirps has a corresponding envelope;transmitting, using a transmitter, a signal corresponding to the chirpsignal; and a modulating the transmitted signal, using a modulationcircuit, wherein modulating the transmitted comprises regulating amagnitude of one or more portions of the chirp envelopes in apredetermined pattern.

In accordance with another example of this disclosure, a non-transitorycomputer readable medium stores instructions executable by a processor,wherein the instructions comprise instructions to: generate a chirpsignal using an oscillation circuit, wherein the chirp signal comprisesa plurality of chirps, and wherein each of the chirps has acorresponding envelope; transmit a signal corresponding to the chirpsignal from a transmitter; and cause a modulation circuit to modulatethe transmitted signal by regulating a magnitude of one or more portionsof the chirp envelopes in a predetermined pattern.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a vehicle equipped with radar sensors, in accordancewith an example of this disclosure.

FIG. 2 is a block diagram of a driver-assistance system, in accordancewith an example of this disclosure.

FIG. 3 illustrates a radar system, in accordance with an example of thisdisclosure.

FIG. 4 is a block diagram of a radar system, in accordance with anexample of this disclosure.

FIG. 5 is another block diagram of a radar system, in accordance with anexample of this disclosure.

FIG. 6 illustrates aspects of a radar system, in accordance with anexample of this disclosure.

FIG. 7 illustrates a method of operating a radar system, in accordancewith an example of this disclosure.

FIG. 8 illustrates aspects of a method of detecting radar interference,in accordance with an example of this disclosure.

FIGS. 9A-B illustrate aspects of a method of minimizing radarinterference, in accordance with an example of this disclosure.

FIGS. 10A-B illustrate aspects of the method of minimizing radarinterference of FIGS. 9A-B.

FIG. 11A is a radar image produced without the benefit of the method ofminimizing radar interference of FIGS. 9A-B.

FIG. 11B is a radar image produced with the benefit of the method ofminimizing radar interference of FIGS. 9A-B.

The accompanying drawings and following detailed description do notlimit the disclosure, but on the contrary, they provide the foundationfor understanding all modifications, equivalents, and alternativesfalling within the scope of the appended claims. Specificconfigurations, parameter values, and examples are explanatory, notrestrictive.

DETAILED DESCRIPTION

In accordance with one or more examples of this disclosure, regulationof signal envelopes is used to improve the efficiency of powerconsumption by radar transmitters. In at least one example, regulationof chirp signal envelopes is used to improve the efficiency of powerconsumption by radar transmitters.

In some examples, regulation of signal envelopes is used to mitigateradar-to-radar interference. In at least one example, enveloperegulation is used to reduce interference caused by one or morenon-linear regions of chirped radar signals in a manner that isefficient with regard to power consumption. In at least one example ofthis disclosure, signal envelope regulation reduces the false detectionrate of radar receivers. In some examples, false detection due a targetecho's interference is minimized.

In one or more examples of this disclosure, a radar transmitter includesa phase rotator, a bi-phase modulator, a variable gain amplifier, aswitch, a power amplifier driver, a power amplifier, a digital signalprocessor (DSP). In at least one example, a radar transmitter alsoincludes a digital controller. In some examples, one or more digitalcontrollers are included in the DSP. In at least one example, the phaserotator is used for digital phase modulation. In some examples, a radartransmitter uses a wave modulated power amplifier in a digital envelopemodulation scheme. In at least one example, a power amplifier is driveninto saturation mode to enable envelope modulation of the poweramplifier. In at least one example, the saturation mode is a class ABsaturation mode. In at least one example, the saturation mode is a classB saturation mode. When operating in saturation mode, the poweramplifier's output envelope has a linear relationship with the poweramplifier's supply voltage. In at least one example, a power amplifierhas a cascade topology in which, the bias voltage at the drain of thepower amplifier's common source transistor tracks the variation insupply voltage. In at least one example, the bias voltage is close tohalf of the supply voltage.

In at least one example of this disclosure, envelope modulation anddemodulation in a radar transmitter is imposed from chirp to chirp usingthe DSP. In some examples, the DSP resides on a chip. In accordance withone or more examples of this disclosure, demodulation occurs after arange fast Fourier transform (FFT) operation is performed. In someexamples, a demodulated envelope pattern is compared or correlated withan original modulating signal. In at least one example, when thedemodulated signal corresponds to a false echo, even if the demodulatedsignal has the same frequency of the transmitted signal after a therange FFT operation, the demodulated signal will not match the envelopecoding pattern of the transmitted signal, making the signalcorresponding to the false echo distinguishable from a signal whichoriginated at the radar transmitter and was reflected by a target.

FIG. 1 shows an illustrative vehicle 102 equipped with an array of radarantennas, including antennas 104 for short range sensing (e.g., for parkassist), antennas 106 for mid-range sensing (e.g., for monitoring stop &go traffic and cut-in events), antennas 108 for long range sensing(e.g., for adaptive cruise control and collision warning), each of whichmay be placed behind the front bumper cover. Antennas 110 for shortrange sensing (e.g., for back-up assist) and antennas 112 for mid-rangesensing (e.g., for rear collision warning) may be placed behind theback-bumper cover. Antennas 114 for short range sensing (e.g., for blindspot monitoring and side obstacle detection) may be placed behind thecar fenders. Each antenna and each set of antennas may be grouped in oneor more arrays. Each array may be controlled by a radar array controller(205). Each set of antennas may perform multiple-input multiple-output(MIMO) radar sensing. The type, number, and configuration of sensors inthe sensor arrangement for vehicles having driver-assist andself-driving features varies. The vehicle may employ the sensorarrangement for detecting and measuring distances/directions to objectsin the various detection zones to enable the vehicle to navigate whileavoiding other vehicles and obstacles.

FIG. 2 shows an electronic control unit (ECU) 202 coupled to the variousultrasonic sensors 204 and a radar array controller 205 as the center ofa star topology. Other topologies including serial, parallel, andhierarchical (tree) topologies, are also suitable and contemplated foruse in accordance with the principles disclosed herein. The radar arraycontroller 205 couples to the transmit and receive antennas in the radarantenna array 106 to transmit electromagnetic waves, receivereflections, and determine a spatial relationship of the vehicle to itssurroundings. The radar array controller 205 couples to carrier signalgenerators. In at least one example, the radar array controller 205controls the timing and order of actuation of a plurality of carriersignal generators.

To provide automated parking assistance, the ECU 202 may further connectto a set of actuators such as a turn-signal actuator 208, a steeringactuator 210, a braking actuator 212, and throttle actuator 214. ECU 202may further couple to a user-interactive interface 216 to accept userinput and provide a display of the various measurements and systemstatus.

Using the interface, sensors, and actuators, ECU 202 may provideautomated parking, assisted parking, lane-change assistance, obstacleand blind-spot detection, autonomous driving, and other desirablefeatures. In an automobile, the various sensor measurements are acquiredby one or more ECU 202, and may be used by the ECU 202 to determine theautomobile's status. The ECU 202 may further act on the status andincoming information to actuate various signaling and controltransducers to adjust and maintain the automobile's operation. Among theoperations that may be provided by the ECU 202 are various driver-assistfeatures including automatic parking, lane following, automatic braking,and self-driving.

To gather the necessary measurements, the ECU 202 may employ a MIMOradar system. Radar systems operate by emitting electromagnetic waveswhich travel outward from the transmit antenna before being reflectedtowards a receive antenna. The reflector can be any moderatelyreflective object in the path of the emitted electromagnetic waves. Bymeasuring the travel time of the electromagnetic waves from the transmitantenna to the reflector and back to the receive antenna, the radarsystem can determine the distance to the reflector and its velocityrelative to the vehicle. If multiple transmit or receive antennas areused, or if multiple measurements are made at different positions, theradar system can determine the direction to the reflector and hencetrack the location of the reflector relative to the vehicle. With moresophisticated processing, multiple reflectors can be tracked. At leastsome radar systems employ array processing to “scan” a directional beamof electromagnetic waves and construct an image of the vehicle'ssurroundings. Both pulsed and continuous-wave implementations of radarsystems can be implemented.

FIG. 3 shows an illustrative radar system 300 having a MIMOconfiguration, in which J transmitters are collectively coupled to Mtransmit antennas 301 to send transmit signals 307. The M possiblesignals 307 may variously reflect from one or more targets to bereceived as receive signals 309 via N receive antennas 302 coupled to Preceivers. Each receiver may extract the amplitude and phase or traveldelay associated with each of the M transmit signals 307, therebyenabling the system to obtain N*M measurements (though only J*P of themeasurements may be obtained concurrently). The processing requirementsassociated with each receiver extracting J measurements can be reducedvia the use of time division multiplexing and/or orthogonal coding. Theavailable antennas are systematically multiplexed to the availabletransmitters and receivers to collect the full set of measurements forradar imaging.

FIG. 4 illustrates a radar transceiver circuit 400 (e.g., 300) in blockdiagram form, in accordance with an example of this disclosure. In atleast one example, the radar transceiver circuit 400 is implemented asan integrated circuit in a packaged chip. Radar transceiver circuit 400includes a carrier signal generator 404, a transmission filter 420, anamplifier 412, and transmit antennas 301 which can transmit signals 307(e.g., chirps 409) based on the output of the carrier signal generator404. Radar transceiver circuit 400 also includes receiver antennas 302,a low noise amplifier 413, and a mixer 407. Mixer 407 mixes signals(e.g., 411) detected by antennas 302 with the signal from the carriersignal generator 404. Low noise amplifier 413 is used to amplify signals411 detected by antennas 302. Radar transceiver circuit 402 alsoincludes a sensitivity time controller and equalizer 413, a broadbandfilter 415, an analog-to-digital converter 417 and a processor 419(e.g., 202, 205). The processor 419 and low noise amplifier 413 can becoupled for bi-directional communication as shown.

In examples of this disclosure, carrier signal generator 404 is coupledto the radar array controller 205. Carrier signal generator 404 includesa chirp generator to create a frequency-modulated continuous-wave (FMCW)signal. The chip rate of the carrier signal generator 404 may becontrolled by the radar array controller 205. In at least one example,the carrier signal generator 404 can be deactivated by the radar arraycontroller 205 to provide an unmodulated carrier signal. The carriersignal generator 404 may be implemented as a local oscillation (LO)signal generator as a fractional-N phase lock loop (PLL) with a ΣΔcontroller, or as a direct-digital synthesis generator.

Carrier signal generator 404 is connected to transmit antennas 301through transmission filter 420 and amplifier 412. Carrier signalgenerator 404 is connected to receiving antennas 302 through mixer 407and low noise amplifier 413. Carrier signal generator 404 generates asignal (e.g., a chirp signal). Amplifier 412 receives the signal fromcarrier signal generator 404 and a transmission signal 307 correspondingto the signal from carrier signal generator 404 is transmitted usingtransmit antennas 301.

As noted, examples of this disclosure pertain to envelope modulation ofchirp signals. In at least one example, an envelope coded FMCWtransmitted signal at the frequency of ƒ_(RF)(t) is given by:s _(t)(t)=A(t)e ^(j(2πƒ) ^(RF) ^((t)t+) ⁰ ^(+φ) ^(d) ^((t))),  (1)where j=√{square root over (−1)}, φ₀ is initial phase, and φ_(d) (t) isphase variation due to Doppler shift, which is given by:

$\begin{matrix}{{{\varphi_{d}(t)} = {{2\pi f_{d}t} = \frac{2\pi f_{RF}{vt}}{c_{0}}}},} & (2)\end{matrix}$where v is a target's (e.g., 305) velocity and c₀ is speed of light.A(t) is an analog baseband envelope signal that is converted by a DACfrom a digital baseband signal generated by a radar DSP unit 419. A(t)is given by:A(t)=Σ_(i=0) ^(N−1) A _(i)(t−iT _(c)),  (3)where A_(i) is the analog scale of FMCW signal that is generated by theDAC from the digital signal α_(i,q−1)α_(i,q−2) . . . α_(i,1)α_(i,0), andT_(c) is chirp period. The reflected signal 309 received is given by:s _(r)(t)=αA(t−τ)e ^(j(2πƒ) ^(RF) ^((t−τ)+φ) ⁰ ^(+φ) ^(d) ^((t))),  (4)where τ is the time delay of the reflected signal 309 and α is theattenuation factor corresponding to free-space propagation loss andradar system loss. After mixing with the LO signal of s_(lo)=e^(jω)^(RF) ^(t), s_(r)(t) is down-converted to an intermediate-frequency (IF)signal, as given by:S _(IF)(t)=αA(t−τ)e ^(j(2πƒ) ^(IF) ^(+φ) ⁰ ^(+φ) ^(d) ^((t))),  (5)in which ƒ_(IF)=ƒ_(RF)(t)−ƒ_(RF)(t−τ). In at least one example of thisdisclosure, the maximum detection range of FM-CW radar ensures thatτ<<T_(c). Thus, the following relationship holds:A(t−τ)≈A(t),  (6)

The relationship of equation no. 6 implies that the magnitude pattern ofthe reflected signal well matches with the magnitude pattern of thetransmitted signal after analog rescaling. In at least one example ofthis disclosure, analog magnitude rescaling is performed before envelopepattern matching because received signals have magnitude levels whichvary in relation the target from which they were reflected. In one ormore examples of this disclosure, each of M generated IF signals isindividually transformed into the spectrum domain by applying the FFT.This processing can be called range FFT processing. Then, MC slices ofthe range FFT spectrums are obtained with respective to MC time stamps,e.g., T_(c), 2T_(c), . . . MC(T_(c)). Then, the maxima and minima of themagnitude of each peak (see e.g., A₀, A₁, A₂ in FIG. 8) over the M timestamps are detected and rescaled to be between zero and unity with thesame number of levels used for the DAC in the envelope modulation. In atleast one example of this disclosure, a transmitted radar waveform frameconsists of MC chirps and the magnitude of each chirp signal isquantized into 2^(Q) levels as represented by a Q-bit digital signal,making the length of the transmitted signal's envelope pattern Q×MC. Fordetected signals, each magnitude peak in the range FFT spectrum producesan identical envelope pattern over MC time stamps for real targets afterthe rescaling. But for interfering sources, the envelope pattern willnot match the transmitted signal. In at least one example, once falsetargets are recognized as such, data samples associated with those falsetargets in the range FFT spectrum are nulled before a velocity FFT isperformed on the captured data, thereby preventing false targets fromappearing in the velocity data.

FIG. 5 illustrates a radar system 500 (e.g., 300, 400) in block diagramform, in accordance with an example of this disclosure. In at least oneexample, the radar system 500 is implemented as an integrated circuit ina packaged chip. The radar system 500 includes a transmitter 502 and areceiver 504 coupled to a signal generator 404. The transmitter 502 andthe receiver 504 are coupled to the processor 419. As shown, theprocessor 419 can comprise a DSP and one or more digital controllers506.

The transmitter 502 includes a phase rotator circuit 508, a bi-phaseshift key modulator circuit 510, a variable gain amplifier (VGA) 512, aswitch 514, and an envelope regulator circuit 516. The enveloperegulator circuit 516 includes a power amplifier 518, an envelopemodulation circuit 520, and a driver 522. The driver 522 is connected toa DC voltage supply 524. In at least one example of this disclosure, theenvelope modulation circuit 520 includes a digital-to-analog converter(not shown). The envelope modulation circuit 520 receives digital signalcontrol signals 521 (e.g., digital baseband signals) from the processor419. The envelope modulation circuit 520 outputs an analog signal A(t)524 to one or more power amplifiers 518. The transmitter 502 is coupledto a plurality of transmit antennas 301 by the one or more poweramplifiers 518. In one or more examples of this disclosure, the transmitantennas 301 transmit signals (307) having an envelope pattern (see 621,FIG. 6).

The radar system 500 includes a plurality of receive antennas 302 whichare coupled to a mixer 407 by low noise amplifier 526 and low noiseamplifier 528. The phase rotator circuit 508 receives an oscillation(LO) signal 523 from the oscillation circuit 404. The mixer 407 receivesa duplicate of the oscillation signal. The mixer 407 mixes theoscillation signal with the signals (309) detected by the receiveantennas 302. The mixed signal 530 passes through a high pass filter532, a low pass filter 534, and an intermediate frequency (IF) amplifierto the processor 419.

In at least one embodiment, the processor 419 generates and sends adigital baseband signal 521 to the envelope modulator 520. Adigital-to-analog converter (e.g., 625) of the envelope modulator 520converts the baseband signal 521 to an analog envelope signal (notshown), which the envelope modulator 520 scales. The scaled analogenvelope signal 524 is received by power amplifier 518. Power amplifier518 outputs a signal 519 for transmission to the transmit antenna 301.The envelope of signal 519 is modulated by the analog envelope signal524 from the envelope modulator 520, and thus tracks the digital signal521 from the processor.

FIG. 6 illustrates aspects of a radar system 600 (e.g., 300, 400, 500)in accordance with an example of this disclosure. The radar system 600includes an envelope modulator 602 (e.g., 520), a power amplifier driver604 (e.g. 522), and a power amplifier output circuit (e.g., 518). Theenvelope modulator 602 includes an operational amplifier 608 connectedto a DSP 610 (e.g., 419). The DSP 610 sends a digital signal 612 toinput 614 of operational amplifier 608. In at least one example of thisdisclosure, the digital signal 612 from the DSP 610 modulates the outputof the operational amplifier 608.

The power amplifier driver 604 receives an input voltage 618 across afirst input terminal 620 and a second input terminal 622. In at leastone example, the voltage 618 across the input terminals 620, 622 comesfrom a signal source through switch (514). The first input terminal 622is connected to a capacitor C_(1p). Capacitor C_(1p) is connected to thegate terminal 624 of a NMOS transistor MN_(1p), and a resistor R_(b1n).The second input terminal 622 is connected to a capacitor C_(1n).Capacitor C_(1n) is connected to a resistor R_(b1p), and the gateterminal 626 of a NMOS transistor MN_(1n). Resistor R_(b1n) and resistorR_(b1p) are both connected to a first DC voltage source V_(B1).

The drain terminal 628 of NMOS transistor MN_(1p) is connected to aninductor L_(1p). The drain terminal 630 of NMOS transistor MN_(1n) isconnected to an inductor L_(1n). Inductor L_(1p) and inductor L_(1n)connected to one another and to local ground 632. The power amplifierdriver 602 also includes a DC voltage source V_(DD1). DC voltage sourceV_(DD1) is connected to a center cap terminal 634 of an inductor L₃ anda first charging capacitor C_(c1). A first output terminal 636 ofinductor L₃ is connected to the power amplifier output circuit 606 atcapacitor C_(2p). The first output terminal 636 of inductor L₃ is alsoconnected to the source terminal 6388 of NMOS transistor MN_(2p). Thedrain terminal 640 of NMOS transistor MN_(2p) is connected to the sourceterminal 642 of NMOS transistor MN_(1p) via inductor L_(2p). The secondoutput terminal 644 of inductor L₃ is connected to the source terminalof NMOS transistor MN_(2n). The drain terminal of NMOS transistorMN_(2n) is connected to the source terminal 646 of NMOS transistorMN_(1n) via inductor L_(2n). The second output terminal 644 of inductorL₃ is also connected to the power amplifier output circuit 606 at acapacitor C_(2n). The gate terminal 648 of NMOS transistor MN_(2p) isconnected to the gate terminal 650 of NMOS transistor MN_(2n) via DCvoltage source V_(B2).

The output terminal 652 of operational amplifier 608 is connected to thegate terminal 654 of PMOS transistor MP₁. The source terminal 656 ofPMOS transistor MP₁ is connected to DC voltage source V_(DD2) and to acharge capacitor C_(c3), which is in turn connected to local ground 632.The drain terminal 658 of PMOS transistor MP₁ is connected to the centercap terminal 660 of inductor L₆ and to a second charge capacitor C_(c2),which is in turn connected to local ground 632. The drain terminal 658of PMOS transistor MP₁ is also connected to input terminal 662 ofoperational amplifier 608. The input terminal 662 of operationalamplifier 608 and the drain terminal 658 of PMOS transistor MP₁ are alsoconnected to resistor R_(2a) and resistor R_(2b). Resistor R_(2b) isconnected to local ground 632. Resistor R_(2a) and resistor R_(2b) areconnected to a first (non-inverting) input terminal 664 of a secondoperational amplifier 666. The output terminal 668 of operationalamplifier 666 is connected to the power amplifier circuit 606 at thegate terminal 670 NMOS transistor MN_(2p) and the gate terminal 672 ofNMOS transistor MN_(2n). The negative input terminal 674 of operationalamplifier 666 is connected to the drain terminal 676 of NMOS transistorMN_(4p) via resistor R_(1p), and connected to the drain terminal 678 ofNMOS transistor MN_(4n) via resistor R_(1n). Resistor R_(1p) is alsoconnected to inductor L_(5p), which connects NMOS transistor MN_(4p) andresistor R_(1p) to the source terminal 680 of NMOS transistor MN_(3p).Resistor R_(1n) is connected to the source terminal 682 of NMOStransistor MN_(3n) via inductor L_(5n). The drain terminal 684 of NMOStransistor MN_(3n) and the drain terminal 686 of NMOS transistor MN_(3p)are connected to one another and to local ground 632. Capacitor C_(2p)is connected to the gate terminal 688 of NMOS transistor MN_(3p) and toa first output terminal 690 of inductor L_(M4). Capacitor C_(2n) isconnected to a second output terminal 692 of inductor L_(M4). The centercap terminal 694 of inductor L_(M4) is connected to DC voltage supplyV_(B3). A first output terminal 696 of inductor L₆ is connected thesource terminal of NMOS transistor MN_(4p) and inductor L_(7p). InductorL_(7p) is connected to a first output terminal 698 via capacitor C_(3p).A second output terminal 601 of inductor L₆ is connected to the sourceterminal of NMOS transistor MN_(4n) and inductor L_(7n). Inductor L_(7n)is connected to a second output terminal 603 via capacitor C3 n. Theoutput 605 across terminal 698 and terminal 603 is an envelope regulatedchirp signal 607 (e.g., 309). The envelope size of the first chirp 609corresponds to a first (intermediate) binary value 611 of the signal 612from DSP 610. The envelope size of the second chirp 613 corresponds to asecond (lower) binary value 615 of the signal 612 from DSP 610. Theenvelope size of the third chirp 617 corresponds to a third (greater)binary value 619 of the signal 612 from DSP 610. The chirp signal 607has an envelope pattern which tracks the signal 612 coming out of DSP610.

DSP 610 generates digital baseband envelope signal 612 which isconverted to corresponding analog signal 623 by digital-to-analogconvertor 625. The analog envelope signal 623 is then received atterminal 614 of amplifier 608. The voltage signal 660 at the center tapterminal 660 of inductor L6 tracks the signal 612 (623). Meanwhile, thesignal at the positive terminal 664 of the amplifier 666 is half thesignal value 660 by using a resistor divider R_(2a) and R_(2b) and thevoltage value 670 tracks the voltage value 660 with half its scale,ensuring that PA 606 operates at an optimal condition. Eventually, theenvelope of the signal 605 tracks the signal 612.

FIG. 7 illustrates a method 700 of operating a radar system (e.g., 300,400, 500, 600) in accordance with an example of this disclosure. Themethod 700 includes generating 702 an FM-CW signal 704. An envelopebaseband signal 707 is generated 704. One copy of the envelope basebandsignal 707 is subjected 708 to pulse shaping filtering. The filteredsignal 709 and the FM-CW signal 704 are then regulated 710 to produce asignal (e.g., 307, 607) which is transmitted 712 to detect the presenceof one or more targets (305).

Signal regulation 710 can include suppressing one or more non-linearportions of a transmit signal (307) from an antenna (e.g., 114) of afirst transmitter (e.g., 502) to reduce interference with signalstransmitted by other antennas (e.g., 110) of that first transmitter.Signal regulation 710 can include suppressing one or more non-linearportions of a transmit signal (307) from an antenna (e.g., 114) of thefirst transmitter (e.g., 300) to reduce interference with signalstransmitted by other antennas (e.g., 110) of a second (different)transmitter. In at least one example of this disclosure, the firsttransmitter and the second transmitter are of different radar systems(e.g., 500). Signal regulation 710 can additionally or alternativelyinclude imposing an envelope pattern (621) on one or more portions of atransmit signal (307). Thereafter, the radar system detects one or moresignals (309). The detected 714 signal (309) could be solely reflectedby a target (305) or the detected 714 signal (309) could includeextraneous signals (e.g., random noise, echo). The detected 714 signal(309) is converted 716 to a digital signal and FFT operations areperformed 718, producing a modified signal 722. A determination is made720 as to whether an envelope pattern (621) was applied 710 to thetransmitted signal (307). If an envelope pattern (621) was applied 710to the transmitted signal (307), the modified signal 722 is rescaled anddemodulated 724. The patterns of the demodulated signal 726 and theenvelope baseband signal 707 are then analyzed 728, and a determinationis made 730 as to whether the patterns of signal 707 and signal 726match (are statistically similar above a threshold). If signals 707 and726 match, a velocity FFT operation is performed 734 on the demodulatedsignal 726. If signals 707 and 726 do not match, the demodulated signal726, now identified as extraneous by the method 700 is nulled 732, andthe method 700 proceeds perform 734 velocity FFT operations onnon-extraneous portions of signal 722.

If it was determined 720 that envelope modulation was not applied duringsignal regulate 710, then signal 722 is subjected 734 to velocity FFToperations outright, as no demodulation is necessary. In either case,once velocity FFT operations are applied 734, the method produces 736data concerning the target's (305) range and the target's (305)velocity. The method 700 can end or the method 700 can proceed tocontinue to generate 702 an FM-CW signal for target detection asdescribed above.

In one or more examples of this disclosure, the radar system (e.g., 300,400, 500, 600) is configured to perform MIMO operations. In one or moreexamples of this disclosure, the radar system (e.g., 300, 400, 500, 600)is configured to perform beam steering operations.

FIG. 8 illustrates aspects of a method 800 (e.g. 700) of detecting radarinterference, in accordance with an example of this disclosure. Atransmitter (e.g., 502) transmits a signal 802 (307) comprising chirpswhose amplitudes are regulated to different levels corresponding todifferent values (e.g., binary numbers). The stream of values makes upthe envelope pattern 805 of the transmit signal 802). In method 800, asignal (309) is also detected (714) and, based on the detected signal(309), an intermediate frequency (IF) signal such as IF1 804 or IF2 806is produced (722). The IF signal (e.g., 804, 806) is rescaled 801. Therescaled 801 (values of the) IF signal, such as IF1 809 or IF2 810, arecompared to outgoing signal 802. If the values 803 of the properlyscaled IF signal (e.g., 809) have the same pattern (621) as the outgoingsignal 802, then the detected signal (309) corresponds to a real target(305). If, on the other hand, the values 807 of the properly scaled IFsignal (e.g., 810) do not have the same pattern (621) as the outgoingsignal 802, then the detected signal (309) is from a false target.

FIGS. 9A-B illustrate aspects of a method 900 of minimizing radarinterference, in accordance with an example of this disclosure. Themethod involves regulating the envelope of a transmitted chirp signal901 (307) of a first transmitter/antenna by suppressing a non-linearportion (e.g., 910) of the transmitted signal 901 using a square wave908 generated by a modulator (e.g., 520) of the first transmitter. Thenon-linear portion of the transmit signal 901 has the potential tointerfere with a signal 904 emitted by a different transmitter/antenna.The non-linear portion of the transmit signal 901 has the potential tointerfere with a signal 904 emitted by a different transmitter/antennaduring the time period(s) 906 in which the second signal 904 (asreflected by a target) is sampled by an ADC (e.g., 417) of a receiver(e.g., 504) corresponding to the different transmitter/antenna.

FIGS. 10A-B illustrate aspects of the method 900 of minimizing radarinterference of FIGS. 9A-B. Time domain signal 1000 corresponds tounregulated frequency domain signal 901. The darker regions (e.g., 1004)of the time domain signal 1000 correspond to the non-linear (resettling)portions 910 of frequency domain signal 901. Time domain signal 1002corresponds to regulated frequency domain signal 902. The regions (e.g.,1006) of the time domain signal 1002 in which the amplitude is close tozero (e.g., 1006), correspond to the suppressed (zeroed) portions 910 offrequency domain signal 902.

FIG. 11A illustrates a radar image 1102 corresponding to a transmitterwhose transmit signal (904) has been interfered with by an interferingsignal (e.g., 901).

FIG. 11B is a radar image 1104 produced with the benefit of the method900 of minimizing radar interference. Radar image 1104 corresponds to atransmitter whose transmit signal (904) has not been interfered with byan interfering signal (e.g., 901).

Examples of this disclosure include:

1. A transceiver system, comprising: a local oscillator configured togenerate a chirp signal, wherein the chirp signal comprises a pluralityof chirps, and wherein each of the chirps has a corresponding envelope;a transmitter, wherein the transmitter is configured to transmit asignal corresponding to the chirp signal; and a modulation circuit,wherein the modulation circuit is configured to modulate the transmittedsignal by regulating a magnitude of one or more portions of the chirpenvelopes in a predetermined pattern.

2. The transceiver system of example 1, further comprising: a receiverconfigured to detect one or more signals; and a processor configured todetermine whether one or more detected signals has a pattern whichmatches the predetermined pattern of the transmitted signal.

3. The transceiver system of example 1, wherein regulating the magnitudeof one or more portions of the chirp envelopes in the predeterminedpattern comprises: setting a magnitude of one or more first envelopes inaccordance with a first integer value; and setting a magnitude of one ormore second envelopes in accordance with a second integer value, whereinthe first integer value is different from the second integer value.

4. The transceiver system of example 3, wherein the first integer valueand the second integer value correspond to binary numbers.

5. The transceiver system of example 1, wherein each of the chirps has acorresponding width, and wherein the modulation circuit is furtherconfigured to truncate a width of one or more of the chirps by imposinga rectangular wave on the chirp signal.

6. The transceiver system of example 5, wherein imposing the rectangularwave on the chirp signal sets a value of a non-linear portion of thetransmitted signal to zero.

7. The transceiver system of example 1, wherein each of the chirps has acorresponding width, and wherein the modulation circuit is furtherconfigured to truncate a width of one or more of the chirps by applyinga window function to the chirp signal.

8. A signal modulation method, comprising: generating a chirp signalusing a local oscillator, wherein the chirp signal comprises a pluralityof chirps, and wherein each of the chirps has a corresponding envelope;transmitting, using a transmitter, a signal corresponding to the chirpsignal; and a modulating the transmitted signal, using a modulationcircuit, wherein modulating the transmitted comprises regulating amagnitude of one or more portions of the chirp envelopes in apredetermined pattern.

9. The signal modulation method of example 8, further comprising:detecting one or more signals at a receiver; and determining, at aprocessor, whether one or more detected signals has a pattern whichmatches the predetermined pattern of the transmitted signal.

10. The signal modulation method of example 8, wherein regulating themagnitude of one or more portions of the chirp envelopes in thepredetermined pattern comprises: setting a magnitude of one or morefirst envelopes in accordance with a first integer value; and setting amagnitude of one or more second envelopes in accordance with a secondinteger value, wherein the first integer value is different from thesecond integer value.

11. The signal modulation method of example 10, wherein the firstinteger value and the second integer value correspond to binary numbers.

12. The signal modulation method of example 8, the method furthercomprising reducing a width of one or more of the chirps by imposing arectangular wave on the chirp signal.

13. The signal modulation method of example 12, wherein imposing therectangular wave on the chirp signal sets a value of a non-linearportion of the transmitted signal to a fixed value.

14. The signal modulation method of example 8, further comprisingreducing a width of one or more of the chirps by applying windowfunction to the chirp signal.

15. A non-transitory computer readable medium storing instructionsexecutable by a processor, wherein the instructions compriseinstructions to: generate a chirp signal using an oscillation circuit,wherein the chirp signal comprises a plurality of chirps, and whereineach of the chirps has a corresponding envelope; transmit a signalcorresponding to the chirp signal from a transmitter; and cause amodulation circuit to modulate the transmitted signal by regulating amagnitude of one or more portions of the chirp envelopes in apredetermined pattern.

16. The non-transitory computer readable medium of example 15, whereinthe instructions further comprise instructions to: detect one or moresignals using a receiver; and determine whether one or more detectedsignals has a pattern which matches the predetermined pattern of thetransmitted signal.

17. The non-transitory computer readable medium of example 15, whereinregulating the magnitude of one or more portions of the chirp envelopesin the predetermined pattern comprises: setting a magnitude of one ormore first envelopes in accordance with a first integer value; andsetting a magnitude of one or more second envelopes in accordance with asecond integer value, wherein the first integer value is different fromthe second integer value.

18. The non-transitory computer readable medium of example 17, whereinthe first integer value and the second integer value correspond tobinary numbers.

19. The non-transitory computer readable medium of example 15, whereinthe instructions further comprise instructions to cause the modulationcircuit to truncate a width of one or more of the chirps by imposing asquare wave on the chirp signal.

20. The non-transitory computer readable medium of example 19, whereinimposing the square wave on the chirp signal sets a value of anon-linear portion of the transmitted signal to zero.

21. The non-transitory computer readable medium of example 15, whereinthe instructions further comprise instructions to cause the modulationcircuit to truncate a width of one or more of the chirps by applying awindow function to the chirp signal.

22. The non-transitory computer readable medium of example 16, whereinthe window function comprises a Hann function or a Blackman function orboth.

Though the operations described herein may be set forth sequentially forexplanatory purposes, in practice the method may be carried out bymultiple components operating concurrently and perhaps evenspeculatively to enable out-of-order operations. The sequentialdiscussion is not meant to be limiting. Moreover, the focus of theforegoing discussions has been radar sensors, but the principles areapplicable to any pulse-echo or continuous-wave travel time measurementsystems. These and numerous other modifications, equivalents, andalternatives, will become apparent to those skilled in the art once theabove disclosure is fully appreciated. It is intended that the followingclaims be interpreted to embrace all such modifications, equivalents,and alternatives where applicable.

What is claimed is:
 1. A transceiver system, comprising: a local oscillator configured to generate a chirp signal, wherein the chirp signal comprises a plurality of chirps, and wherein each of the chirps has a corresponding envelope; a transmitter, wherein the transmitter is configured to transmit a signal corresponding to the chirp signal; and a modulation circuit, wherein the modulation circuit is configured to modulate the transmitted signal by regulating a magnitude of one or more portions of the chirp envelopes in a predetermined pattern, wherein the modulation suppresses a non-linear portion of the transmitted signal to zero or a fixed value.
 2. The transceiver system of claim 1, further comprising: a receiver configured to detect one or more signals; and a processor configured to determine whether one or more detected signals has a pattern which matches the predetermined pattern of the transmitted signal.
 3. The transceiver system of claim 1, wherein regulating the magnitude of one or more portions of the chirp envelopes in the predetermined pattern comprises: setting a magnitude of one or more first envelopes in accordance with a first integer value; and setting a magnitude of one or more second envelopes in accordance with a second integer value, wherein the first integer value is different from the second integer value.
 4. The transceiver system of claim 3, wherein the first integer value and the second integer value correspond to binary numbers.
 5. The transceiver system of claim 1, wherein each of the chirps has a corresponding width, and wherein the modulation circuit is further configured to truncate a width of one or more of the chirps by imposing a rectangular wave on the chirp signal.
 6. The transceiver system of claim 1, wherein the non-linear portion of the transmitted signal is associated with resettling.
 7. The transceiver system of claim 1, wherein each of the chirps has a corresponding width, and wherein the modulation circuit is further configured to truncate a width of one or more of the chirps by applying a window function to the chirp signal.
 8. A signal modulation method, comprising: generating a chirp signal using a local oscillator, wherein the chirp signal comprises a plurality of chirps, and wherein each of the chirps has a corresponding envelope; transmitting, using a transmitter, a signal corresponding to the chirp signal; and a modulating the transmitted signal, using a modulation circuit, wherein modulating the transmitted comprises regulating a magnitude of one or more portions of the chirp envelopes in a predetermined pattern, wherein the modulation suppresses a non-linear portion of the transmitted signal to zero or a fixed value.
 9. The signal modulation method of claim 8, further comprising: detecting one or more signals at a receiver; and determining, at a processor, whether one or more detected signals has a pattern which matches the predetermined pattern of the transmitted signal.
 10. The signal modulation method of claim 8, wherein regulating the magnitude of one or more portions of the chirp envelopes in the predetermined pattern comprises: setting a magnitude of one or more first envelopes in accordance with a first integer value; and setting a magnitude of one or more second envelopes in accordance with a second integer value, wherein the first integer value is different from the second integer value.
 11. The signal modulation method of claim 10, wherein the first integer value and the second integer value correspond to binary numbers.
 12. The signal modulation method of claim 8, the method further comprising reducing a width of one or more of the chirps by imposing a rectangular wave on the chirp signal.
 13. The signal modulation method of claim 8, wherein the non-linear portion of the transmitted signal is associated with resettling.
 14. The signal modulation method of claim 8, further comprising reducing a width of one or more of the chirps by applying window function to the chirp signal.
 15. A non-transitory computer-readable storage medium for use with an electronic device, the computer-readable storage medium storing instructions executable by a processor, wherein, when executed by the processor, the instructions cause the electronic device to perform operations comprising: generating a chirp signal using an oscillation circuit, wherein the chirp signal comprises a plurality of chirps, and wherein each of the chirps has a corresponding envelope; transmitting a signal corresponding to the chirp signal from a transmitter; and causing a modulation circuit to modulate the transmitted signal by regulating a magnitude of one or more portions of the chirp envelopes in a predetermined pattern, wherein the modulation suppresses a non-linear portion of the transmitted signal to zero or a fixed value.
 16. The non-transitory computer-readable storage medium of claim 15, wherein the operations further comprise: detecting one or more signals using a receiver; and determining whether one or more detected signals has a pattern which matches the predetermined pattern of the transmitted signal.
 17. The non-transitory computer-readable storage medium of claim 15, wherein regulating the magnitude of one or more portions of the chirp envelopes in the predetermined pattern comprises: setting a magnitude of one or more first envelopes in accordance with a first integer value; and setting a magnitude of one or more second envelopes in accordance with a second integer value, wherein the first integer value is different from the second integer value.
 18. The non-transitory computer-readable storage medium of claim 17, wherein the first integer value and the second integer value correspond to binary numbers.
 19. The non-transitory computer-readable storage medium of claim 15, wherein the operations further comprise causing the modulation circuit to truncate a width of one or more of the chirps by imposing a square wave on the chirp signal.
 20. The non-transitory computer-readable storage medium of claim 15, wherein the non-linear portion of the transmitted signal is associated with resettling.
 21. The non-transitory computer-readable storage medium of claim 15, wherein the operations further comprise causing the modulation circuit to truncate a width of one or more of the chirps by applying a window function to the chirp signal.
 22. The non-transitory computer-readable storage medium of claim 21, wherein the window function comprises at least one of a Hann function or a Blackman function. 